High yield getter device

ABSTRACT

A getter device capable of providing large amounts of active getter material comprising a pan-shaped container for holding pressed getter material and an auxiliary heating means at least partially buried in said pressed getter material.

United States Patent Inventor Clair W. Reash Fairview Park, Ohio Appl. No. 783,029 Filed Dec. 1 1, I968 Patented Jan. 26, I971 Assignee Union Carbide Corporation New York, N.Y. a corporation of New York HIGH YIELD GE'ITER DEVICE 1 Claim, 4 Drawing Figs.

US. Cl 313/180, 313/174; 206/04 Int. Cl 1101i 19/70 Field of Search 313/174, 180; 206/O.4

I I I I I I Primary ExaminerRaymond F. I-Iossfeld Attorneys-Paul A. Rose, Thomas I. OBrien, Harrie M.

Humphreys and Leo A. Plum ABSTRACT: A getter device capable of providing large amounts of active getter material comprising a pan-shaped container for holding pressed getter material and an auxiliary heating means at least partially buried in said pressed getter material.

PATENTEU JAN26 1971 3; 558.962

saw 2 f 2 3/, H i 1 i 24 F/G.4 Z4 25 v 28 Z9 Z6 20 INVI'IN'I'UR.

CLAIR W. REASH ATTORNEY HIGH YIELD GETTER DEVICE This invention relates to a high yield getter device for use in electron tubes and particularly in television picture tubes.

The use of the getter materials in the manufacture of electronic tubes is well known. A commonly used getter construction consists of a container, such as an annular U-shpaed receptacle, with the getter material pressed into the container. This assembly is mounted in an electron tube, for example, a television picture tube. After the tube is evacuated, the residual gases left in the tube are removed by heating the getter container and material therein to a high temperature, suitably by induction heating, whereupon the getter material is flashed or vaporized. The vaporized getter material adsorbs or reacts with the residual gases and removes them as low vapor pressure solid condensates and continues to adsorb any further liberated gases throughout the life of the tube.

Usually the getter material comprises a mixture or alloy of metals such as, for example, barium and aluminum. It is the barium component of this mixture which comprises the reactive material. The cleanup of residual gases in the larger sized television picture tubes, and particularly color tubes, requires a relatively large amount of active barium material. For example, color tubes having three electron guns and a metal shadow mask have been considered in the past to require a yield of l25to 175 mg. of barium. Since the barium-aluminum powder mixture might have contained up to about 50 percent aluminum, the total amount of gettering powder mixture in the container before flashing could be from 250 to 350 mg. It has also been found desirable to employ exothermic gettering powders in color television picture tubes. An exothermic gettering powder can comprise a barium-aluminum alloy or mixture plus about an equal weight of powdered nickel. The nickel reacts exothermically with the aluminum upon heating to supply additional heat for evaporating the barium as well as to assist in forming a solid residue of the unflashed material which remains in the container.

A typical channel ring exothermic getter used in color television tubes may contain, for example, 500 mg. of a 25 percent barium25 percent aluminum-50 percent nickel exothermic alloy yielding about 125 mgs. of barium when fully flashed. The getter container itself may comprise a U-shaped channel formed into a ring of about 25 mm. outside diameter and having a channel width of about 0.1 inch. To fulfill a need for a barium yield greater than 125 mg., getter containers of the above dimensions can be filled with an increased amount of barium-aluminum-nickel alloy, say 600 mgs. instead of 500 mg., and a barium yield of about 150 mg. will be obtained. lfa barium yield significantly in excess of this amount is required, then the length of the channel, and hence the diameter of the ring would have to be increased; or the width or height of the channel would have to be increased. Because of the manner of utilizing the getter container in the tube and because of the getter flashing conditions, it has been found impractical to significantly increase either the diameter of the container or the width or height of the channel for the reasons set out hereafter.

An electron tube, particularly a television picture tube, generally comprises a neck portion in which are located the electron gun or guns and auxiliary equipment; an enlarged bulb portion which terminates in a generally flat viewing screen; and a funnel portion joining the neck and bulb portions. The getter container is often mounted in the funnel portion of the tube. This is accomplished by mounting the getter container at the end of a springlike metallic strip support arm or antenna, the other end of which is fixed to a wall of the electron gun in the neck portion of the tube. The spring is biased to force the getter container against the wall of the tube in the funnel portion, out of the path of the electron beams. An RF induction heating unit comprising a coil spirally wound in a conical shape which approximates the curve of the tube wall in the funnel area is positioned near this wall of the glass tube opposite the getter container. After the tube is partially evacuated by vacuum pumping and sealed, the coil is energized causing an induced current to flow in the getter container, heating the container and flashing the getter material.

In order to mount the getter container in the funnel portion of the tube, it is necessary to pass the container through the neck portion of the tube into the funnel section. The diameter of this passageway is limited by an internal ridge often found in the tube at thejuncture of the neck and funnel portions due to flow of the fused glass during the joining of the neck and funnel portion. it has been found inconvenient to use getter containers over 25 mm. outer diameter because of this passageway limitation. This is especially the case in regard to the insertion in the tube of getter containers which have understructures designed to support the container off the wall of the tube to prevent direct contact of the heated container with the cooler walls of the tube so that cracking of the tube will not occur.

It is therefore not generally feasible to increase the barium capacity of getter containers of the channel-ring type merely by increasing their outer diameter. Additionally, while the capacity of a channel ring getter container can be increased, by widening the channel, it has been found that such containers do not flash effectively because of an incomplete coupling of the RF field to the inner portions of the widened channel member. For example, a getter capacity of about L000 mg. can be obtained by increasing the channel width of a 25 mm. container from 0.l inch to 0.15 inch. However, since the spirally wound coil has an open core, there is a lesser concentration of flux generated at the inner wall of a 0.15 inch wide channel with the result that a lesser heating current is induced in the getter and an incomplete flashing of barium takes place. These problems regarding limitation on the size and configuration of getter containers apply to even the large 25 inch color tubes. At the same time, there is a demand for getters of significantly greater barium yield than the presently available getters for use in these large 25 inch tubes whereby the life of such tubes can be increased by providing additional getter material therein.

It is the primary object of this invention therefore to provide a high yield getter which is insertable into present day electron tubes and which can be effectively flashed to provide maximum amounts of reactive getter material.

According to the present invention, a high yield getter is provided for mounting in an electron tube against an inner wall thereof and containing getter material to be flashed by induction heating of said getter by circular RF field produced by an induction coil positioned externally of said tube wall and opposite said mounted getter, said getter comprising a metallic pan-shaped container having a vertical sidewall formed around the perimeter of a floor member with getter material pressed into the space formed by said sidewall and floor member, and an auxiliary heating means at least partially buried in said pressed getter material for conducting heat into the mass of said pressed getter material.

In one embodiment of the invention, the auxiliary heating means comprises a perforated metallic member overlying the container floor member and being buried in the mass of pressed getter material intermediate the top and bottom surfaces thereof, with getter material present in the perforations of said metallic member.

In a specific embodiment of the invention, the high capacity getter may comprise a pan-shaped container having a vertical sidewall formed around a flat circular floor member, a discshaped piece of metallic screen lying in the space formed by the sidewall and floor member, said screen joined to the underlying floor member at one or more points, and getter material pressed into said space at least partially burying said screen.

In the drawings:

1 is a schematic view of the neck and funnel portions of a television picture tube, in cross section, including the getter device of this invention mounted in the antenna" position and showing the positioning of the heating coil;

FIG. 2 is a plan view of a high yield getter container of this invention showing the disc-shaped screen in place on the floor member but prior to filling of the container with getter material;

FIG. 3 is an end view of the getter container of FIG. 2;

FIG. 4 is a sectional view along the line 4-4 of FIG. 1, but showing getter material pressed into the container.

Referring to FIG. 1 there is shown a portion of a typical glass television picture tube. Such a tube may be viewed as having three main parts: a neck portion 11; a funnel portion 12; and the bulb or a main tube, only a portion 13 of which is shown. The central axis 6 of the tube extends through these parts. It is of course understood that the division of a tube into such parts is arbitrary and it is not meant here that the getter of this invention can only be'used in a funnel portion of a tube. Under suitable circumstances, the getter of this invention could be mounted nearer to the gun in the neck of the tube or further into the bulb of the tube as desired. Additionally, it is to be understood that the getter of this invention can be used in other typed of electron tubes than the television picture tube described herein and can also be used in other types of evacuated vessels.

More specifically, an electron gun 14 (or guns in the case of a color tube) is shown positioned in the neck of the tube. An antenna spring or support arm 15 is shown fixed at one end 16 to the sidewall of the gun and having mounted on its opposite end 17 the getter container 18. The support arm 15 is a piece of thin, flexible, flat metal strip, such as for example stainless steel or a nickel-base alloy, biased to urge the getter container 18 against the wall 19 of the tube and out of the path of the electron beam. The getter container is supported in a position out of direct contact with the glass wall of the tube by a support member such as 20, otherwise the glass wall might crack if it were contacted directly by the hot getter container.

An RF induction heating coil 21 is shown positioned near the outer wall of the funnel portion of the tube. The coil and getter container must be arranged symmetrically so that the heating currents induced in the getter containers are uniform and symmetrical. The RF field generated by this coil can be viewed as comprising elliptical .flux lines, the long sides of which loop through the open central core of the coil, being more concentrated at the inner periphery of the individual windings of the coil and increasingly less dense nearer the center axis of the coil. The flux lines then flow around the outside of the coil. Referring again to FIG. 1, the arrow 22 represents the central axis of the coil as well as the getter container. Portions of the elliptical flux lines are represented schematically by the lines 23. Because of the nature of the high frequency RF coil, the diameter of its smallest winding being greater than the diameter of the getter container, and because of the interposition of the getter container in the RF field, the flux lines in the vicinity of the getter container are most concentrated at the periphery of the circular container, as represented by the lines 23. The heating currents induced in the getter container are therefore most concentrated in circular patterns near the periphery of the container where these outer portions of the getter container intercept the flux lines. The central portion of the getter container is thus not heated as effectively as the outer portion with the result that there would be incomplete flashing of the getter material in this central portion of the container in the short time allowed for heating the container.

Referring now to FIGS. 2 through 4, an improved getter is shown which overcomes the above-disclosed difficulties. As seen there, the getter container 24 has a continuous vertical sidewall 25 formed around a circular floor member 26 forming a pan-shaped receptacle into which getter material may be pressed. A metallic screen 27 cut into the shape of a disc of a diameter slightly less than the diameter of the pan is placed in the container and joined thereto, as by several spot welds, for example at the center of container 28 and at several other points 29. The getter material 30 can then be pressed into the container so as to cover the screen 27 and fill the various openings in and under the screen, as shown in FIG. 4. A mounting bar 31 extends across the underside of the container and is welded to the floor member, for example at points 32 and 33. A wire support member 20 may be welded at its midpoint 34 to the underside of the mounting bar 31. The antenna support arm 15 is connected at its'end I7 to the projecting tab 35 on the mounting bar and the getter container mounted in the tube with the wire support member 20 resting on the tube wall.

The screen 27 serves as an auxiliary heating means during the getter flashing operation as follows: when the induction coil is energized and the getter container heated, the portions of the screen which are at the periphery of the getter con tainer, i.e., near the sidewall 25, take heat from this outer annular portion of the container and conduct it radially inward into the mass of getter material near the center 28 of the container. As a result, this central mass of getter material receives more heat than if there were no screen present. While the container floor member 26 also conducts heat from its outer portions in towards its center, this member only contacts the bottom surface of the packed mass of getter material. The screen 27, being at least partially buried in the mass of getter material, contacts additional portions of the mass of pressed getter material and transmits heat to these regions as well. The getter material in the center of the container is thus more effectively heated to a flashing temperature and the barium vapor is discharged in a substantially uniform pattern over most areas of the container.

The screen 27 is a metallic mesh of interwoven metal wires. Other types of perforated members may be used as the auxiliary heating means. They need only be metallic to conduct the heat to the central mass of gettermaterial, and should have perforations so as to allow getter material to be in close contact with this heating member and so that the member does not occupy too much of the space in the container which is primarily intended to hold getter material. The auxiliary heating member should extend from the peripheral areas of the getter container near the sidewall to the center of the container. In this way, the auxiliary heating member can take heat from the peripheral areas where the RF flux is densest and where the heating effect is greatest, and transmit such heat to the central mass of the getter container where the flux density is least and where the induction heating is lowest. By means of this arrangement, getter containers holding large amounts of getter material are provided which yield reactive barium getter material in the same manner and with substantially the same efficiency as the more typicalchannel ring getter containers, despite the negative effects of the circular heating pattern available for flashing getters in television picture tubes. Since the pan-shape getter can hold considerably more getter material in a container no larger than the channel ring getter, an advance in the art is provided whereby additional gettering power is made available for electron tubes without necessitating any costly changes in tube design or getter flashing technique.

Another advantage of the use of a screen member buried in the getter powder, is that the screen serves to hold the pressed getter material together as a coherent mass, particularly during and after flashing. The screen acts as a reinforcing means and holds the getter residue in the container after flashing, preventing the ejection of any solid particles into the tube interior where such foreign bodies might interfere with operation of the electronic system. This is so even in those cases where the screen is not actually welded to the floor of the container. For example, the getter material may be partially pressed into an empty getter container, and then a disc-shaped screen placed over the powder and pressed thereinto. The screen, despite its lack of direct contact with the outer portions of the floor member will still become highly heated at its outer portions and will conduct heat into the central mass of getter material. Furthermore the screen, while only pressed into the surface of the powder and not directly anchored to the container, will fuse into the powder on heating and will bind the residue together preventing ejection of particles.

The auxiliary heating member should generally be of a metal which will not melt as a result of the getter heating operation and additionally should be nonmagnetic. Stainless steel mesh, for example SS304, is a suitable material. The stainless steel member, containing nickel and iron, also tends to react exotherrnically at its surfaces with the getter material in the container and therefore aids in directly supplying some of the heat needed to flash the barium. All other portions of the getter containers should be nonmagnetic metals, e.g., stainless steels and other nonmagnetic alloys.

An example of a getter of this invention is a pan-shaped getter container of the type shown in FIGS. 2 through 4 having an outside diameter of about 25 mm. The height of the vertical sidewall is about 0.085 inches. A stainless steel screen of X 10 mesh, i.e., 10 wires per inch, is cut to a diameter slightly less than the inner diameter of the container and inserted therein and spot welded at five points. About 2,000 mg: of barium-aluminum-nickel powder is pressed under high pressure into the screen containing getter receptacle. This powder nominally comprises 25 percent each of barium and aluminum in the form of an alloy, and 50 percent powdered nickel. In practice, the barium-aluminum-nickel contents may be varied from these proportions as desired. When a getter of this type is mounted in a tube, as shown in FlG. 1, and flashed, a yield of barium in excess of 400 mg. may be obtained. Yields of 80 to 85 percent of the barium contained in the getter may be obtained using the arrangement of this invention.

While the invention herein has been described in terms of exothermic barium-aluminum-nickel getter materials, it is of course understood that other getter materials, including endothermic mixtures may be used in the getter containers of this invention.

While the improved getter containers of this invention have been described with regard to their use in large electron tubes, for example 25 inch color T.V. tubes, it is understood that such containers can be produced in various sizes and capacities for use in T.V. picture tubes of any diameter as well as any other evacuated device which requires a getter container of high capacity.

Iclaim:

1. A high yield getter for mounting in the funnel portion of an electron picture tube against a wall thereof for discharging large quantities of active getter material into the tube interior when the getter is heated by currents induced from an RF field created by a coil positioned outside the tube opposite the getter, said getter comprising a pan-shaped container having a vertical sidewall formed around the perimeter of a floor member, a disc-shaped piece of metallic screen lying in the space formed by the sidewall an joined to the floor member with powdered getter material pressed into the space formed by said sidewall and floor member at least partially burying said screen, whereby when the coil is activated the metallic screen serves to conduct heat from the peripheral portions of the container adjacent said sidewall where the induced heating current is most intense into the central mass of the pressed getter materiaLwhere the induced heating current is less intense to provide for uniform flashing of the active contents of the getter material and whereby said metallic screen serves to hold the getter material residue in said container after flashing. 

1. A high yield getter for mounting in the funnel portion of an electron picture tube against a wall thereof for discharging large quantities of active getter material into the tube interior when the getter is heated by currents induced from an RF field created by a coil positioned outside the tube opposite the getter, said getter comprising a pan-shaped container having a vertical sidewall formed around the perimeter of a floor member, a disc-shaped piece of metallic screen lying in the space formed by the sidewall an joined to the floor member with powdered getter material pressed into the space formed by said sidewall and floor member at least partially burying said screen, whereby when the coil is activated the metallic screen serves to conduct heat from the peripheral portions of the container adjacent said sidewall where the induced heating current is most intense into the central mass of the pressed getter material where the induced heating current is less intense to provide for uniform flashing of the active contents of the getter material and whereby said metallic screen serves to hold the getter material residue in said container after flashing. 